JPS61159627A - Liquid crystal electrooptic device - Google Patents

Abstract

PURPOSE:To obtain an excellent memory effect even with a cell having several mum thickness at which mass production is possible by providing ferroelectric layers on electrodes so as to contact with a liquid crystal layer. CONSTITUTION:Transparent electrodes 17, metallic layers 18 and ferroelectric layers 19 are successively formed on glass substrates 14 and the liquid crystal 21 is sandwiched by such substrates via a spacer 20. The layers 19 contact with the liquid crystal 21. The surfaces of the layers 19 are rubbed if a high- polymer ferroelectric material is used for said layer. Parallel grooves are formed by rubbing or etching on the surfaces if an inorg. ferroelectric material is used for said layer. The layers are otherwise not treated in either case.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a substrate surface treatment method in a liquid crystal electro-optical device using a ferroelectric liquid crystal having memory effect, high-speed response, and steep threshold characteristics. .

[Conventional technology]

Conventional substrate surface treatment methods for liquid crystal electro-optical devices include:
A method in which the same type of surface treatment layer such as polyimide is provided on each of the upper and lower substrates, a method in which no treatment is applied at all, a method in which surface treatment layers of the same type such as polyimide are provided on the upper and lower substrates, and a method in which the surface treatment layers have different polarities on the surfaces of the upper and lower substrates as shown in the 10th Liquid Crystal Symposium Proceedings 14A17. There is a method in which polyimide is applied to the surface of the substrate and then a rubbing treatment is performed in the same manner as in the alignment treatment of nematic liquid crystals.

[Problem that the invention seeks to solve]

Smectic b consisting of chiral molecules exhibits ferroelectricity, and as shown in Figure 1, the liquid crystal molecules 11 are always located on a cone with an angle of θ from the z-axis direction, and the liquid crystal molecules 11
It has a permanent dipole 12 in a direction perpendicular to the smectic layer and parallel to the smectic layer (X-Y plane). Therefore, by applying an electric field and changing the direction of the permanent dipole 12, the position (azimuth angle φ) of the liquid crystal molecules 11 on the cone can be controlled. However, 13 is a projection of the liquid crystal molecules 11 onto the XY plane.

The orientation of liquid crystal molecules in the X-Y cross section of a cell several microns thick is shown in FIG. Figure 2 (α), (A)e
(C) shows the orientation of liquid crystal molecules when no electric field is applied, when an electric field of 10E is applied from the lower substrate to the upper substrate, and when an electric field -E is applied, respectively. However, FIG. 2 shows the orientation in a cell in which polyimide 15 is coated on the substrate surface. When there is no electric field, the permanent dipoles 12 are oriented from the substrate surface to the inside of the cell, but by changing the type of treatment agent on the substrate surface, the permanent dipoles 12 are oriented from the inside of the cell toward the substrate when there is no electric field. Such an orientation can also be obtained. The quality of the memory effect is evaluated by the orientation state in the absence of an electric field, and if the same orientation as shown in Figure 2 (A) and (C) is maintained even after the electric field is removed, the memory effect is excellent. It is evaluated that the

The orientation state in the absence of an electric field is strongly influenced by the cell thickness, and the third
As shown in the figure, it seems that various orientations are taken depending on the thickness of the cell. The orientation states of FIG. 3 (eL) to (C) are tw
This state is called the 1st state, and the state shown in FIG. 3(d) is called the untwiat state.

Here, depending on the cell thickness, u at the time of voltage application after the electric field is removed is
The reason why the ntwist state cannot be maintained is considered as follows. There are two types of forces that liquid crystal molecules receive from the substrate surface: the force that tries to hold the liquid crystal molecules parallel to the substrate surface (anchoring force), and the force that is caused by the permanent dipole of the liquid crystal molecules and the polarity of the substrate surface. There is an interaction between If only the anchoring force is considered, both of the two orientation states shown in Figure 4 (α) and (b) are stable, and even after the electric field is removed, the unt is the same as when the electric field is applied.
The wiat state should be preserved. However, if the Coulomb force is taken into account, the energies of the orientations shown in Figure 4 (α) I (A) are different, and if the polarity of the substrate surface is positive, #! 4
The orientation shown in figure (α) is the most stable. Therefore, in this case, after the liquid crystal molecules are oriented as shown in FIG. 4Cb) by applying an electric field, when the electric field is removed, the liquid crystal molecules tend to reverse to the alignment state shown in FIG. 4(α).

The magnitude of the effect of Coulomb force on orientation can be estimated by measuring polarization reversal current.

FIG. 5 shows the polarization inversion current when a triangular electric field is applied to a 4 μm thick cell. When the orientation of the permanent dipole is reversed in response to an electric field, a polarization reversal current flows, as shown in Figure 5<b>.
A peak appears, but as you can see from this figure, the reversal of the permanent dipole begins even before the direction of the electric field is reversed. That is, when the electric field strength becomes smaller than a certain value, the state changes from the state shown in Fig. 4(b) to the state shown in Fig. 4(b) against the electric field.
In order to move to the energetically advantageous state α), the permanent dipole begins to reverse, and the interaction between the permanent dipole and the polarity of the substrate surface is considered to be very strong.

In order for the liquid crystal molecules to reverse from the state shown in Figure 4 (Cb) to (α), they must not be reversed in a plane parallel to the substrate surface, but
In order to rotate and invert around two axes on the cone shown in FIG. 1, one end of the liquid crystal molecules, which was initially oriented parallel to the substrate surface, must rise from the substrate surface. (
(See FIG. 5) It is thought that the degree to which one end of a liquid crystal molecule can lift up from the substrate surface is determined by the balance between the anchoring force and Coulomb force that the liquid crystal molecule receives.

The anchoring force that liquid crystal molecules receive decreases as the distance from the substrate surface increases.As the cell becomes thicker, the distance between the liquid crystal molecules located at a certain distance from one substrate surface and the other substrate surface increases, and The anchoring force that liquid crystal molecules receive from both substrate surfaces is smaller than in the case of a thin cell. Therefore, as the cell becomes thicker, the Coulomb force becomes more dominant than the anchoring force exerted on the liquid crystal molecules.
Various tw1 as shown in FIG. 5 depending on the cell thickness.
The st state becomes stable.

Up to this point, we have explained the phenomenon in a cell where the same type of surface is used for the upper and lower substrates, but when surfaces with different polarities are used for the upper and lower substrates, the untWiat state shown in Figure 6 (cL) is stable. becomes.

For example, 1910. In the cell in which the layer 16 is provided and the polyimide layer 15 is provided on the surface of the lower substrate, the orientation state shown in FIG. 6(α) has the minimum energy and is the most stable, but the orientation state shown in FIG. 6(A) The orientation state shown in is extremely unstable.

In addition, there is a processing method in which a polyimide layer or the like is provided on the surface of the substrate and further a rubbing process is performed. In this case, in addition to the 1-anchoring force and Coulomb force, an alignment force that tries to regulate the alignment of liquid crystal molecules in the rubbing direction is added, making it even more difficult to obtain the memory effect. In either treatment method, the cell thickness must be made sufficiently thin in order to maintain the cell thickness. The critical cell thickness at which the tw1st state no longer appears after the electric field is removed varies depending on the substrate surface treatment method, and is thickest when surface treatment layers of the same polarity are provided on both the upper and lower substrates and no rubbing treatment is performed. However, even with this type of surface treatment method, the critical cell thickness is very thin, less than 1 μm, so it is extremely difficult to create such thin, highly uniform cells even at the laboratory level, and mass production is difficult. The current situation is extremely difficult.

The present invention is intended to solve these problems, and its purpose is to provide a substrate surface treatment method that exhibits an excellent memory effect even in mass-produced cells with a thickness of several μm. .

[Means to solve the problem]

In the substrate surface treatment method of the present invention, a ferroelectric layer is provided on both the upper and lower glass substrate surfaces on which electrodes are provided, and when a polymer ferroelectric is used as the ferroelectric, a rubbing treatment is applied to the surface, and an inorganic When a dielectric material is used, it is characterized in that grooves parallel to its surface are created by rubbing or etching, or in either case it is left untreated.

[Effect]

In the conventional method, it is not possible to arbitrarily control the polarity of the substrate surface after the electric field is removed, but according to the above structure of the present invention, the polarity of the substrate surface is changed depending on the direction of the permanent dipole of the liquid crystal molecules when the electric field is applied. The polarity of the surface is reversed, and since it is ferroelectric, the polarity is maintained even after the electric field is removed, so it is possible to obtain an excellent memory effect even in cells with a thickness of several micrometers that can be mass-produced.

〔Example〕

(Example-1) FIG. 7 shows a cross-sectional view of a liquid crystal electro-optical device in this example. 17 is a transparent electrode, 18 is a platinum layer, 19 is a ferroelectric layer, 20 is a spacer, and 21 is a liquid crystal layer, and the ferroelectric 19 and the liquid crystal 21 are in contact as shown. P-decyloxybenzylid as the ferroelectric liquid crystal 21
en-p'-amino-2-methylbuty
la-1nnamemate (DOB A MBO
) as the ferroelectric material 19, P I, Z T
(9/65155) and the surface remains untreated. The transparent electrode 17! 1not. liquid crystal layer 2
1. The thickness of the ferroelectric layer 19 and the platinum layer 18 are 4.
5 μm duck, 155 μm thickness and 5101 μm duck size.

PLZ'l! The thin film was fabricated by high frequency sputtering. The substrate temperature is approximately 500℃, the sputtering gas is a /75 mixed gas of oxygen and argon, and the target is approximately 8% PbO.
It is an excess amount of FLZ'l' powder.

FIG. 8 shows the hysteresis characteristics (6oag) of a PLZT thin film with a thickness α5μ vortex created by this method. The horizontal axis is &5v/μs/A i V . Compared to the hysteresis characteristic of a single crystal ferroelectric, the rectangularity of the thin film is slightly inferior, but this is due to poor crystallinity at the boundary between the ferroelectric layer 19 and the underlying layer (platinum layer 18). . That is, the boundary layer does not exhibit ferroelectricity, and the magnitude of polarization changes in response to changes in electric field strength, resulting in the characteristics shown in FIG. 8. However, in the present invention, since it is sufficient that at least the surface layer of the ferroelectric material exhibits ferroelectricity, the thickness of the ferroelectric material is made thicker than the boundary layer with poor crystallinity. If the thickness of the ferroelectric material in the layer is made thicker than the boundary layer with poor crystallinity so that the surface layer of the ferroelectric material has ferroelectricity, it can be used for the purpose of the present invention. However, the thickness of this boundary layer depends on the substrate temperature during sputtering.

FIG. 9 shows an alignment model of liquid crystal molecules for each electric field strength in this example. 1B is a platinum layer, 19 is a ferroelectric layer, and arrow 22 represents a permanent dipole of the ferroelectric surface layer. In Fig. 9 (α) to (-), the electric field strength is +51! It corresponds to i, O, -E, -511f, and O. From FIG. 9, it can be seen that by providing the ferroelectric layer 19 on the upper and lower substrates, the two unts remain the same even after the electric field is removed as when the electric field is applied.
It can be seen that the vist state (9th vA(α), (d)) is stable.

FIG. 10 is a diagram showing whether the memory effect is good or bad.

FIG. 10 (α) shows the applied pulse voltage, and (h)*(C) shows the change in transmitted light intensity with respect to the applied pulse voltage. The peak value vtsvx of the applied pulse voltage is a value that can completely switch between the two untviat states shown in FIG. 9 (α) and (41). The difference in brightness after removing the voltage can be evaluated by 1' and II- by l, and the smaller the values of p-p0/ and p3-dzheng, the better the memory effect.

Figure 10 (b'J is the change in transmitted light intensity in this example. For comparison, Figure 10 (C) shows the transmitted light intensity in a cell with a 1.5 μm thick groove created by the conventional method. Comparing the two, it can be seen that the memory effect obtained in this example is very excellent.

The threshold characteristic for a pulse voltage with a pulse width of 100μ is very steep, and 790/V10 = 1-1 (Vα
: the voltage required for the transmitted light intensity to change by α%), and the steepness was comparable to that of the conventional technology. Also, the contrast (of SIR/ ) is 1:2 using white light.
0 was obtained.

(Example 2) The structure was the same as that of the first example, and the thickness of the liquid crystal layer and the ferroelectric layer were each 50 μWLIrL8μ. This example also has an excellent memory effect, with 790/'V 1
0 = 1.2 m A contrast of 1:23 was obtained.

(Example 5) The structure was the same as that of the first example, and the thicknesses of the liquid crystal layer and the ferroelectric layer were each 1.5 μ'a l and 1.0 μm. The memory effect was also excellent in this implementation, with V90/V1
0=1.1, :'/) The last time was 1:35.

(Example 4) In this example, a BaT103 sputtered thin film with a thickness of 1.0 μm was used, with the liquid crystal layer having a thickness of &2 μm and 1 ferroelectric layer. The liquid crystal material is B-4-0-(2-methyl
) butyl -resoroyil@no-
4'-allC-yLaniline (M B R
Mu-8). The B a T i O@ thin film was sputtered at a substrate temperature of about 650° C. and heat-treated at about 850° C. for 4 hours. This example also has an excellent memory effect, with 79
0/710:1.15.

A contrast of 1:23 was obtained.

(Example-5) In this example, p-aecyloxyb was used as the liquid crystal material.
e-ngyliiene -p' -amino-
1-methylbutylc-1nnamate (
7 as a ferroelectric material.
Bithenidene tsulfide/ethylidene trifluoride D1P (/) copolymer was used.Thickness ?r7K VD? is &5μm and 15μm, respectively. /Tram
The thin film was prepared by dissolving a copolymer having a composition of 74/26 in methyl ethyl ketone and spinning the solution.

After film formation, rubbing treatment was performed, and further heating at 100°C for 1 s
≠-ring was performed by applying an electric field of OMY/, Il. FIG. 11 shows the V D IF /
Hysteresis characteristics of T r 7111 thin film (601i
z). The horizontal axis is 40v/μm/(L i W
It is. This example also has an excellent memory effect,
A T90/"I 1 G" 1-1 e contrast of 1:25 was obtained.

As described above, excellent memory effects were obtained even in cells as thick as 1 μm or more. Ferroelectric material is P Xs
Z T e B & T i Os * V D I
The present invention is not limited to F/Tr IPB, and similar results can be obtained using other ferroelectric materials, and the film thickness is not limited.

When creating a ferroelectric thin film, if the substrate temperature is too low, the resulting thin film will not exhibit ferroelectricity, but the critical temperature depends on the type of underlying substrate, and if platinum is used as the underlying substrate, the critical temperature will be will be relatively low. Therefore, in the above embodiment, the platinum layer 18 is provided as shown in FIG.
A platinum layer is not necessarily required. In addition, when applied as a matrix addressing device, the electrodes are striped, but there is no need to pattern the ferroelectric layer in the same shape as the electrodes, and the ferroelectric layer is patterned over the entire surface of the upper and lower substrates as shown in Figure 7. That's fine.

〔effect〕

As described above, according to the present invention, the memory effect, which was conventionally obtained only in thin cells of about 1 μm or less, can be achieved with a thickness of several μm.
Since it can be obtained even in a cell with a size of 1.5 m, it has the effect that a large-area liquid crystal electro-optical device using ferroelectric liquid crystal, which was impossible with conventional techniques, can be easily manufactured.

[Brief explanation of drawings]

Figure 1g: i is a diagram showing the positional relationship between liquid crystal molecules, permanent dipoles, and two axes, Figures 2 (g) to (c) are X of a sacrificial cell with a thickness of several μ
-A diagram showing liquid crystal molecule orientation in the Y cross section, Figure 5 (α)
-(d) are diagrams showing the orientation of liquid crystal molecules in cells of various thicknesses, and FIG. 4(a). Cb) is a diagram showing the interaction between the permanent dipoles of liquid crystal molecules and the polarity of the substrate surface; Figures 5(a) and 5(b) are diagrams showing polarization reversal current when a triangular wave electric field is applied; Figure 6 (α
)*Cb) is a diagram showing the orientation state when surfaces with different polarities are used for the upper and lower substrates, Figure 7 is a diagram showing the configuration of a liquid crystal cell according to the present invention, and Figure 8 is a diagram showing the PLZT fabricated by sputtering. A diagram showing the hysteresis characteristics of thin films, Figure 9 (
α) to Cg) are diagrams showing the orientation state of polarization of liquid crystal molecules and ferroelectric material for each applied electric field when a ferroelectric layer is used, and FIGS. FIG. 11 is a diagram showing the hysteresis characteristics of vinylidene fluoride/ethylene trifluoride copolymer. 11...Liquid crystal molecule 12---One permanent dipole 15...Projection of liquid crystal molecule onto the X-Y plane 14.
...Glass substrate 15--Polyimide 16--f910! 17...Transparent electrode-18...Platinum 19...Ferroelectric material 20...Spacer 21...Liquid crystal 22... ...More than the polarization of the ferroelectric surface layer

Claims (2)

[Claims] (1) A liquid crystal in which a ferroelectric liquid crystal is sealed between two glass substrates provided with electrodes, and polarizing plates are provided above and below the two glass substrates so that the polarization axes are substantially perpendicular to each other. 1. A liquid crystal electro-optical device, characterized in that a ferroelectric layer is provided on the electrode so as to be in contact with a liquid crystal layer. (2) The liquid crystal electro-optical device according to claim 1, wherein the ferroelectric layer is always provided on both of the two glass substrates.